The present invention relates to a vacuum servomotor activated in response to an electric output signal from an electric control system, such as an electronic rotation speed control system for a vehicle engine, and more particularly to a vacuum servomotor in which a solenoid valve is provided to modulate vacuum within a servo chamber of the servomotor in response to an electric signal.
In such a conventional vacuum servomotor, a spring loaded armature is attracted to a magnetic pole by energization of a solenoid winding to operate the solenoid valve. With the mechanical construction of the servomotor, it is observed that attraction of the armature to the pole inevitably causes unpleasant impact noises due to abutment of two metallic pieces and that after deenergization of the solenoid winding, retraction of the armature from the pole is disturbed by residual magnetism of the pole.